Evidence of Evolution

◼ The Fossil Record

◼ Similarities in Development

◼ Similarities in Body Structure

◆ Homologous structures

◆ Vestigial structures

◆ (Analogous structures)

◼ Biochemical Compounds

The Fossil Record

◼ Fossils preserve evidence of past life forms

◆ Hard parts (shell, bone) preserved better

◆ Chancy process

◆ Quality varies

◼ Fossils trapped in sedimentary rock layers: age of layers can be determined

Further reading: textbook section 13-3

The Fossil Record

Further reading: textbook section 13-3

◼ Embryo: organism at early stage of development

◼ Similarities of vertebrate embryos → similar genes at work responsible for patterning of body segments

◼ Mutations that disrupt development are lethal; selected against

◼ Early developmental stages retained evolutionarily

Similarities in Development

◼ Homologous Structures: body structures that

appear different and meet different needs, but have

common origin. Indicates common ancestry.

Similarities in Body Structure

◼ Vestigial Organs: organs that serve no useful

function in an organism

◆ E.g. humans: wisdom teeth, appendix,

tailbone, tonsils

◆ E.g. pelvic bone in whale and snake, eyes in

star-nosed mole

Similarities in Body Structure

◼ Analogous Structures: structures that appear

similar and have similar functions, but the

evolutionary origin is different. These organisms

DO NOT share a common ancestor.

◆ E.g. bat wing and butterfly wing

◆ E.g. mimicry in wing patterns

◼ Darwin was not aware of biochemical evidence

◼ Some biochemical compounds conserved

evolutionarily: essential and/or ‘as good as it gets’

◆ DNA/RNA as genetic material

◆ Cytochrome c (used in mitochondrial electron transport

chain)

◆ Rubisco in all photosynthetic organisms (Calvin cycle)

Biochemical Compounds

Biochemical Compounds

◼ Darwin was not aware of biochemical evidence

◼ Some biochemical compounds conserved

evolutionarily: essential and/or ‘as good as it gets’

◆ DNA/RNA as genetic material

◆ Cytochrome c (used in mitochondrial electron transport

chain)

◆ Rubisco in all photosynthetic organisms (Calvin cycle)

Artificial/natural selection only works on variation that

already exists. Variation on essential components likely

to be bad (selected against).

Biochemical Compounds

Analogy to TechnologyNot testable

Analogy to TechnologyNot testable

Descent with Modification

◼ Living organisms evolved through gradual

modification of earlier forms – descent from a

common ancestor

Summary of Darwin’s Theory

1) Variation exists in nature: individuals differ from one another in their traits

Summary of Darwin’s Theory

2) Struggle for Existence

◼ Because more organisms are produced than

can survive, each species must struggle for

resources

◼ Each organism is unique: each has

advantages and disadvantages in the

struggle for existence

Summary of Darwin’s Theory

2) Survival of the fittest

◼ Individuals best suited for the environment

are most successful at surviving and

reproducing; they pass on their traits

(adaptations)

Summary of Darwin’s Theory

3) Evolution

◼ Frequency of variants of traits in a species

or population changes over time

◼ “Process by which modern organisms have

descended from ancient organisms”

Summary of Darwin’s Theory

4) Descent with Modification/Common

Ancestry

◼ Species alive today descended with

modification from species that lived in the

past

◼ All organisms on earth are united into a

single family tree of life by common

descent

MISCONCEPTIONS

#1: “Individuals adapt or mutate in order

to survive/reproduce in the environment”

◼ No! This sounds Lamarckian.

◼ New adaptations or mutations only very rarely

arise, and never with a ‘purpose’ or ‘goal’…only

randomly

◼ No adaptation or mutation occurs during lifetime;

you must be born with it (it is inherited from your

parents)

#2: “Natural selection occurs

because of variation in fitness”

◼ Variation = different types, different traits,

different “variants” in population

◼ Variation in traits → variation in fitness →

different individuals survive and reproduce more

◼ Selection acts on the variation in traits that already

exists

#3: “Natural selection only happens

when environment changes”◼ Natural selection is happening all the time; the key

is an individual’s ability to survive and reproduce

(its fitness)

◼ Sometimes the environment is stable (in

equilibrium)…frequencies of traits unlikely to

shift

◆ E.g. brown and white mice living happily together

◼ Sometimes environment changes. When change

occurs, the frequency of certain traits is likely to

shift

◆ E.g. frequency of white mice decreases

#4: “After natural selection, new

traits/adaptations appear”

◼ New adaptations or mutations only very rarely

arise, and never with a ‘purpose’ or ‘goal’…only

randomly

◼ The only result of natural selection is that the

variants who are most fit, pass on their traits more;

overall there is a change in frequency of these

traits to favour the most adaptive traits (i.e. those

that increase fitness)

#5: “Unfit individuals do not

reproduce”

◼ They may still reproduce, but they reproduce less

than the more fit individuals

#6: “Long lifespan helps them look

after offspring”

◼ Longer lifespan linked to more offspring (higher

reproductive rate)

◼ May be related to offspring care, but not

necessarily

◆ E.g. humans must live long to take care of

young

◆ E.g. plants, coral, jellyfish, fish do not take care

of young (generally)